An embodiment relates generally to permanent magnet motors.
A permanent magnet synchronous motor is an AC motor in which the rotation rate of the shaft is synchronized with the frequency of the AC supply current. A rotating electric field is generated in the stator and the rotor follows the rotating electrical field of the stator. The rotor rotates in step with the field of the stator at a same rate. The rotor and the stator are said to be in synchronization.
The permanent magnets used in conventional rotors are configured to provide a specified alternating magnetic field distribution in the air gap. In an effort to reduce the amount of rare-earth magnets, some machines utilize a permanent magnet assist synchronous reluctance machine structure utilizing cheaper ferrite magnets. These machines are constructed using straight or curved permanent magnets embedded in the rotor core; with as many as 8 to 10 magnets per pole requiring up to 5 different sets of tooling. Moreover, the costs to manufacture these magnets are expensive, and assembly within the rotor may be difficult based on the shape and size of the magnets.
Another approach to reducing the amount of rare-earth magnets is to use a conventional spoke-type rotor construction. However, the rotor structure for a conventional spoke-type rotor is a multi-piece construction utilizing a plurality of individual components to assemble and couple the rotor structure together particularly using pins and rods to reduce mechanical stress encountered during elevated speed operations of the motor.